Muffle furnace



i. r ii -A Delaware application March 15, 194e, serial No. 324,115

1 claim. (ci.` 23-277) This invention relates to the manufacture of hydrochloric acid and sodium sulfatev in mechanical furnaces of the Mannheim type, and has for its object the elimination of scale formation on the hearth of such furnaces.-

The principles and operation of the invention may best be understood vby reference to the accompanying drawings in which Figure 1 is a side elevation in section of one type of Mannheim furnace, Figure 2 'is a section taken along line 2 of Figure 1 with parts broken away to show detail, and Figure 3 is a section in elevation taken along line 3 of Figure 2.

Figure 1 illustrates a typical Mannheim furnace whichhas been modied, as will presently be 'pointed out, according to this invention. Mannheim furnaces are in general indirect red from scaling vor caking of the saltcalre (sodium or munie furnaces in which the muflle is in the nature of a vertical cylinder topped by a convex refractory arch I. In some Mannheim furnaces, as illustrated in Figure 1, the bottom of the mullle is composed of an annular hearth 2 of suitable refractory tile surrounding a pot 3 constructed of cast iron or any suitable material- In others the bottom is entirely tile without special configuration describing a pot. The mullle is built in appropriate brick-work structure, as illustrated generally at 4, adapted to direct burner gases from a suitable burner 5 over and in contact with the top of the muflle,

down thru suitable flue 6 and back under the bottom of the muliie, and thence to stack.

In the operation of such furnaces sulfuric acid and salt are charged into the muflle thru the thimble Lin proper portions to yield hydrochloric acid and sodium sulfate. The charge is agitated and progressively moved' towards` the periphery of the mullle by the plows 8 carried by the arms 9 mounted on the vertical shaft I0, the plows 8 being so shaped and positioned as gradually to push the reaction mass out towards the periphery of the mulile. To prevent corrosion of the arms 9 the sulfuric acid is fed by means of the pipe II to the pot I2 which rotates with the arms and has a spout I3 adapted to pass the acid to the pot 3 Without contacting the arms 9.

In the past it has been customary to heat' the mullie both from the top and the bottom or, in

other words, to heat the charge both'by radiation from the top of the mullle and by conduction thru the hearth 2 and the pot 3. It has been considered necessary heretofore vto apply heat to the charge in all ways available in order effectively to carry the reaction to completion. We have now found, however, that indiscrimi- 'bottom of the mulile.

sulfate)' on the hearth, where it interferes with effective operation of the plows and has to be periodically removed. In the past it has been necessary to shut down these furnaces to remove the scale formed on the hearth at intervals of about three weeks and sometimes less.

-According to our present invention we are able to operate under the same conditions over an interval of two to four times as long without having to shut down for removal of scale formation. Even then bottom scale is practically negligible and the shut-downs are required primarily for removal of scale formations from the side Walls only. By eliminating more than one-half of the shut-downs required per year we obtain substantial advantagesin cost of operation, both in respect to the actual cost of the scaling operation and in respect to increased productivity, due to longer periods of uninterrupted operation. We also obain advantages in that damage lto the furnace brickvvork as aresult of frequent cooling and heating is lessened. Likewise'we obtain advantages in that the life of the tile bottom of the inutile, that is, the life of the hearth, is greatly prolonged.

We obtain these advantages by so directing the combustion gases that heat is not applied to the reaction mass thru the hearth. Thus we'l have provided beneath the hearth 2 a layer of insulation I 4 of any suitable refractory insulating material and thereby prevent transfer of heat from the hot gases thru the hearth 2. In this manner the formation of scale on the bottom of the mule is prevented and the capacity of the fur-y nace surprisingly is not decreased as might be expected. Apparently the scale'rwhich rapidly formed on the surface `'of the hearth when heat l Wasapplied thereto acted effectively to prevent any practical utilization of heat from the combustion vgases in that manner.

According to the preferred form of our inventrary we have found it' desirable to concentrate the hqt combustion gases at this point in the common-salt are charged into the furnace the mass is quite uid, due n'ot only to the sulfuric acid but also to the formation of the low melting When sulfuric acidand 2 Y, "acerbes bisulfate. We have found that when the reaction mixture is in this uid state it can be strongly heated-without scale formation. It is only.

' bustion gases upon the pot and excluding them from the hearth we obtain advantages, not only in eliminating the scaling but also in increased fuel efciency, which have not been possible heretofore. l

As illustrated in Figures 2 and 3 at l5 we provide suitable bailles underneath the hearth whereby the hot combustion gases discharged from the ues'S are concentrated under the pot.' In this manner maximum heat efliciency is obtained without the disadvantages ofv scaling o`n the hearth.

While we haveillustrated our inventionA ap' plied to Mannheim furnaces in which the bottom munie is made up of ,a pot 'and 'a hearth, it is 'to be understood that iti is equauy appncame to l. g other types of Mannheim furnaces. `Also, it will be apparent that there is other means which may be adopted for insulating the hearth'from. i

the hotcombustion gases. These and numerous other modifications may' be made without departing from our invention, and such variations as may be made without departing from the spirit and scope thereof are intended to be ineluded in the appended claim.

We claim:

In a hydrochloric` acid furnace of the Mannheim type the combination comprising a munie having a'circular bottom composed of a circular pot and an annular calcining hearth, means for directing hot combustion gases over the top of the mue andlunder the bottom thereof, means for insulating the hearth from said hot combus- Y tion ygases and means for concentrating said hot combustion gases under said pot.

FRED FARMER.'

JAMESF. GARRE'I'I'. 

